Larval retention and recruitment in an island population of a coral-reef fish

For close to a century, recruitment of larvae to a local population has been widely accepted as a primary determinant of marine population dynamics(1,2). However, progress in elucidating the causes of recruitment variability has been greatly impeded by our ignorance of the sources of recruits. Although it is often assumed that recruitment is independent of local reproduction(3-6), there is increasing circumstantial evidence that physical(7,8) and behavioural(9,10) mechanisms could facilitate larval retention near source populations. To develop a direct method for reconstructing the dispersal history of recruiting larvae, we put forward the hypothesis that differences in nutrient and trace-element concentrations between coastal and open oceans could result in quantifiable differences in growth rate and elemental composition between larvae developing in coastal waters (locally retained) and larvae developing in open ocean waters (produced in distant locations). Using this method, we show that recruitment to an island population of a widely distributed coral-reef fish may often result from local retention on leeward reefs. This result has implications for fisheries management and marine reserve design, because rates of dispersal between marine populations-and thus recruitment to exploited populations-could be much lower than currently assumed.